Radiographic image capturing system

ABSTRACT

A radiographic image capturing system includes the following. A capturing stand includes a holder to hold radiographic image capturing devices. A radiation irradiator is able to irradiate the radiographic image capturing devices at once. An image processor generates images based on image data acquired by the radiographic image capturing devices. The image processor removes a structural component derived from the front radiographic image capturing device, on the basis of a calibration image and the generated image. The calibration image is preliminarily generated based on the image data acquired by the rear radiographic image capturing device with no subject disposed. The generated image is generated based on the image data acquired by the rear radiographic image capturing device during actual image capturing. The image processor removes a streaky component residing in the generated image.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention claims priority under 35 U.S.C. §119 to JapaneseApplication No. 2015-082439, filed Apr. 14, 2015, the entire content ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radiographic image capturing system,specifically, a radiographic image capturing system including acapturing stand for capturing a long image by one-shot exposure.

2. Description of Related Art

An example of the recently developed capturing stands for supportingradiographic image capturing devices (flat panel detectors) used forcapturing radiographic images of relatively large areas of a patient,such as a full spine or a full leg, (i.e., a long image) is, forexample, with reference to FIG. 20A, a capturing stand 100 including aholder 101 carrying multiple radiographic image capturing devices P1 toP3 aligned along the body axis A of a patient H (in the verticaldirection in FIG. 20A) (for example, refer to Japanese PatentApplication Laid-Open No. 2012-045159). The number of radiographic imagecapturing devices P to be loaded in the holder 101 is not limited tothree.

Capturing of a long image using such a capturing stand can be carriedout by positioning the patient H and the holder 101 (i.e., theradiographic image capturing devices P1 to P3) and irradiating themultiple radiographic image capturing devices P1 to P3 once via thesubject (i.e., patient H) with radiation from the radiation irradiator102 (i.e., one-shot exposure).

Although not illustrated, traditional capturing of a long image iscarried out by irradiating a single radiographic image capturing deviceP loaded in a holder with radiation multiple times from the radiationirradiator 102 while moving the radiographic image capturing devices P1to P3 in the vertical direction. Unfortunately, the patient could moveduring movement of the radiographic image capturing device P togetherwith the holder. Capturing a long image by one-shot exposure isadvantageous in that such problem due to body movement does not occur.

As illustrated in FIG. 20A, capturing of a long image through a singleexposure of the multiple radiographic image capturing devices loaded inthe holder to radiation with a subject disposed in front of theradiographic image capturing devices is referred to as “capturing a longimage by one-shot exposure.” In the layout of the multiple radiographicimage capturing devices in the holder, the bottom radiographic imagecapturing device P is disposed closer to the radiation irradiator 102compared to the top radiographic image capturing device P in the holder101, as illustrated in FIG. 20A, or the multiple radiographic imagecapturing devices P are staggered in the holder 101 so as to bealternately adjacent to or remote from the radiation irradiator 102, asillustrated in FIG. 20B.

Besides the vertical capturing stand 100 that captures a long image byone-shot exposure of the patient H in an upright position, asillustrated in FIGS. 20A and 20B, a horizontal capturing stand, such asthat illustrated in FIG. 21, may also be used to capture a long image byone-shot exposure with radiation emitted once from above a recumbentpatient H on a top panel 103 disposed above a holder 101 carryinghorizontally aligned radiographic image capturing devices P1 to P3.

With reference to FIGS. 20A, 20B, and 21, edges of the radiographicimage capturing devices P1 to P3 loaded in the holder 101 of thecapturing stand 100 for capturing a long image by one-shot exposureoverlap in view from the radiation irradiator 102. Thus, theradiographic image capturing device P in front from the radiationirradiator 102 is projected on the image acquired by the radiographicimage capturing device P in the back from the radiation irradiator 102.

Among the radiographic image capturing devices loaded in a holder in acapturing stand according to the present invention, the radiographicimage capturing device close to the radiation irradiator is referred toas a front radiographic image capturing device, and the radiographicimage capturing device remote from the radiation irradiator is referredto as a rear radiographic image capturing device, in the case of notonly the holder being installed in the vertical capturing stand 100illustrated in FIGS. 20A and 20B, but also the horizontal capturingstand 100 illustrated in FIG. 21. Thus, the front radiographic imagecapturing device P in the capturing stand 100 illustrated in FIG. 21 isthe top radiographic image capturing device P close to the radiationirradiator 102, and the rear radiographic image capturing device P isthe bottom radiographic image capturing device P remote from theradiation irradiator 102.

With reference to FIG. 22A, an image p1 acquired by the rearradiographic image capturing device P1 (see FIG. 20A) containstransverse streaky components CL caused by linear structures, such asthe edges of the casing and/or inner structure of the front radiographicimage capturing device P2, and structural components CS caused by thestructures in the casing of the front radiographic image capturingdevice P.

With reference to FIG. 22B, an image p2 acquired by the rearradiographic image capturing device P2 contains streaky components CLcaused by linear structures, such as the edges of the casing and/orinner structure of the front radiographic image capturing device P3, andstructural components CS caused by the structures in the casing of thefront radiographic image capturing device P3.

The streaky components CL do not necessarily have a width of one pixeland could have a width of several pixels to several tens of pixels. Thestreaky components CL and the structural components CS in the image p1illustrated in FIGS. 22A and 22B are depicted to contain pixels havingpixel values of 0 for simplicity. Actually, the pixels of the streakycomponents CL and the structural components CS do not have pixel valuesof 0 but pixel values smaller than the original values.

As described above, the image p1 acquired by the rear radiographic imagecapturing device P containing the streaky components CL and thestructural components CS cannot be precisely aligned and combined withthe image p2 acquired by the front radiographic image capturing deviceP. Thus, the images cannot be combined to generate a long image.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention, which has been conceived to solvethe problem described above, is to provide a radiographic imagecapturing system that can acquire images by one-shot exposure that canbe precisely corrected and combined to generate a long image.

According to an aspect of the present invention, there is provided aradiographic image capturing system including: a capturing stand whichincludes a holder which is able to hold a plurality of radiographicimage capturing devices; a radiation irradiator which is able toirradiate the radiographic image capturing devices loaded in the holderat once with radiation; and an image processor which generates aplurality of images based on image data acquired by the radiographicimage capturing devices, wherein, an edge of a front radiographic imagecapturing device overlaps in an anteroposterior direction with an edgeof a rear radiographic image capturing device in the holder in view fromthe radiation irradiator, the front radiographic image capturing devicebeing a radiographic image capturing device close to the radiationirradiator among the radiographic image capturing devices loaded in theholder, the rear radiographic image capturing device being aradiographic image capturing device remote from the radiation irradiatoramong the radiographic image capturing devices loaded in the holder, theimage processor removes a structural component derived from the frontradiographic image capturing device projected on a generated image, onthe basis of a calibration image and the generated image, thecalibration image being preliminarily generated based on the image dataacquired by the rear radiographic image capturing device irradiated withradiation with no subject disposed in front of the radiographic imagecapturing devices loaded in the holder of the capturing stand, thegenerated image being generated based on the image data acquired by therear radiographic image capturing device during actual image capturingof a subject, and the image processor removes a streaky componentresiding in the generated image on the basis of the generated image, tocorrect the image.

According to another aspect of the present invention, there is provideda radiographic image capturing system including: a capturing stand whichincludes a holder which is able to hold a plurality of radiographicimage capturing devices; a radiation irradiator which is able toirradiate the radiographic image capturing devices loaded in the holderat once with radiation; and an image processor which generates aplurality of images based on image data acquired by the radiographicimage capturing devices, wherein, an edge of a front radiographic imagecapturing device overlaps in an anteroposterior direction with an edgeof a rear radiographic image capturing device in the holder in view fromthe radiation irradiator, the front radiographic image capturing devicebeing a radiographic image capturing device close to the radiationirradiator among the radiographic image capturing devices loaded in theholder, the rear radiographic image capturing device being aradiographic image capturing device remote from the radiation irradiatoramong the radiographic image capturing devices loaded in the holder, theimage processor removes a streaky component residing in the generatedimage based on the generated image, to correct the image, and the imageprocessor subtracts a background component from a component acquiredthrough horizontal smoothing of a region assigned in the imagecontaining the streaky component during removal of the streakycomponent, to extract the streaky component, and adds the extractedstreaky component to a pixel value of each pixel in the image, to removethe streaky component from the image.

According to the radiographic image capturing system of the presentinvention, it is possible to acquire images by one-shot exposure thatcan be precisely corrected and combined to generate a long image.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the appended drawings, andthus are not intended to define the limits of the present invention, andwherein;

FIG. 1 illustrates the configuration of a radiographic image capturingsystem according to an embodiment;

FIG. 2 illustrates an example configuration of a radiographic imagecapturing system including multiple capturing rooms linked to at leastone console;

FIG. 3 is a perspective view illustrating the exterior of a radiographicimage capturing device;

FIG. 4 is a block diagram illustrating the equivalent circuit of aradiographic image capturing device;

FIG. 5 illustrates an example configuration of a sensor panel of aradiographic image capturing device;

FIG. 6 illustrates a front radiographic image capturing device and arear radiographic image capturing device in a holder of a capturingstand;

FIG. 7 is a flow chart illustrating the image correction processaccording to an embodiment;

FIG. 8 illustrates an example calibration image;

FIG. 9A illustrates loading positions and dongles disposed on a holderof the capturing stand;

FIG. 9B illustrates a dongle in connection with a connector of aradiographic image capturing device;

FIG. 10 illustrates an example calibration image after adjustment ofpositioning and enlargement factor;

FIG. 11A is a graph illustrating a profile of pixel values of a pixelcolumn in an adjusted calibration image;

FIG. 11B is a graph illustrating a profile of pixel values of a pixelcolumn in a base image;

FIG. 12 illustrates an example region of interest assigned to an areacentered on a target pixel in an image;

FIG. 13A illustrates a corrected image p1 from which structuralcomponents are removed;

FIG. 13B illustrates a corrected image p2 from which structuralcomponents are removed;

FIG. 14 illustrates an example combined image generated throughcombination of images p1 and p2 illustrated in FIGS. 13A and 13B,respectively;

FIG. 15 illustrates an example scheme for extraction of streakycomponents in a region R in a combined image;

FIG. 16 illustrates pixel rows Lp1 and Lp2 selected from the region R;

FIG. 17 illustrates an example long image;

FIG. 18A illustrates the segmentation of a processed combined image;

FIG. 18B illustrates example images from which structural components andstreaky components are removed;

FIG. 19 is a flow chart illustrating another process of imagecorrection;

FIG. 20A illustrates an example configuration of a capturing stand forcapturing a long image by one-shot exposure;

FIG. 20B illustrates another example configuration of a capturing standfor capturing a long image by one-shot exposure;

FIG. 21 illustrates an example configuration of a horizontal capturingstand for capturing a long image by one-shot exposure;

FIG. 22A illustrates streaky components and structural components in animage acquired by the rear radiographic image capturing device caused bythe front radiographic image capturing device projected on the image;and

FIG. 22B illustrates streaky components and structural components in animage acquired by the rear radiographic image capturing device caused bythe front radiographic image capturing device projected on the image.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A radiographic image capturing system according to an embodiment of thepresent invention will now be described with reference to theaccompanying drawings. FIG. 1 illustrates the configuration of aradiographic image capturing system according to this embodiment.

FIG. 1 illustrates a capturing room Ra containing only a capturing stand51A for capturing a long image by one-shot exposure. The capturing roomRa may also contain other capturing stands, such as a vertical capturingstand 51B and a horizontal capturing stand 51C for simple radiography(see FIG. 2). That is, when there is only one capturing room Ra, thecapturing stand 51A for capturing a long image by one-shot exposureshould be installed in the capturing room Ra and any other additionalmodalities may be optionally installed in the capturing room Ra.

The basic configuration of a radiographic image capturing system 50according to this embodiment is illustrated in FIG. 1. One capturingroom Ra is connected to one console C. Alternatively, two or morecapturing rooms Ra (Ra1 to Ra3) may be connected to one or more consolesC (C1 and C2) via a network N, as illustrated in FIG. 2.

In multiple capturing rooms Ra as illustrated in FIG. 2, at least one ofthese capturing rooms Ra should be provided with a capturing stand 51Afor capturing a long image by one-shot exposure, and any otheradditional modality may be optionally installed in the capturing room Racontaining the capturing stand 51A and the other capturing rooms Ra.Alternatively, a capturing stand 51A for capturing long image byone-shot exposure may be installed in all of the capturing rooms Ra.

Hereinafter, the capturing stand 51A for capturing a long image byone-shot exposure may also be simply referred to as “capturing stand51A”. FIGS. 1 and 2 illustrate upright image capturing of a patient (notshown in FIG. 2) standing in front of the capturing stand 51A forcapturing a long image by one-shot exposure. Alternatively, thecapturing stand 51A for capturing a long image by one-shot exposureaccording to the present invention may be applied to recumbent imagecapturing of a patient laying or sitting on a top panel above a holdercarrying multiple radiographic image capturing devices, as illustratedin FIG. 21.

[Configuration of Radiographic Image Capturing System]

With reference to FIG. 1, the capturing room Ra (or at least one of themultiple capturing rooms Ra (see FIG. 2)) according to this embodimentcontains a capturing stand 51A for capturing a long image in a singleexposure, which can hold multiple radiographic image capturing devicesP1 to P3 for capturing a long image. The capturing stand 51A includes aholder 51 a that can carry radiographic image capturing devices P1 to P3aligned along the body axis A of a subject or patient H.

Hereafter, the radiographic image capturing devices P1 to P3 will becollectively referred to as radiographic image capturing devices P,unless they should be differentiated. With reference to FIGS. 1 and 2,loading of three radiographic image capturing devices P in the holder 51a of the capturing stand 51A will now be described. Alternative to threeradiographic image capturing devices P, two, four, or more radiographicimage capturing devices P may be loaded in the capturing stand 51A inthe present invention.

With reference to FIG. 1, multiple radiographic image capturing devicesP are loaded in the holder 51 a such that the lower radiographic imagecapturing devices P (P2 and P3) are disposed closer to the radiationirradiator 52 than the higher radiographic image capturing devices P (P1and P2). Alternatively, multiple radiographic image capturing devices P1to P3 may be staggered in the holder so as to be alternately close to orremote from a radiation irradiator, as illustrated in FIG. 20B.

The capturing room Ra contains the radiation irradiator 52. Withreference to FIG. 1, the radiation irradiator 52 for capturing a longimage is of a wide-angle radiation type that can simultaneously exposethe multiple radiographic image capturing devices P1 to P3 loaded in thecapturing stand 51A through a single exposure (one-shot exposure) of thepatient H as the subject with radiation.

The capturing room Ra is provided with a relay 54 for relaying thecommunication between individual units inside the capturing room Ra andindividual units outside the capturing room Ra. The relay 54 includes anaccess point 53 for wireless transmission of image data D and othersignals from and to the radiographic image capturing devices P1 to P3.In FIGS. 1 and 2, the radiographic image capturing devices P1 to P3,which are loaded in the holder 51 a of the capturing stand 51A, asdescribed above, can be connected to the relay 54 via cables toestablish communication. The relays 54 are connected to a controller 55of the radiation irradiator 52 and the console C.

A console 57 of the radiation irradiator 52 is installed in a frontchamber (operating chamber) Rb, as illustrated in FIG. 1. The console 57includes an exposure switch 56 to be operated by an operator orradiologist to instruct the start of radiation to the radiationirradiator 52.

The front chamber Rb is provided with the console C composed of acomputer (not shown) including a central processing unit (CPU), a readonly memory (ROM), a random access memory (RAM), and an input/outputinterface, connected to each other via a bus. The radiographic imagecapturing system 50 having the configuration illustrated in FIG. 2 mayinclude a console C disposed outside the capturing room.

The console C includes a display unit Ca including a cathode ray tube(CRT) or a liquid crystal display (LCD), and an input unit including amouse and a keyboard (not shown). The console C is connected to anexternal or internal storage unit Cb including a hard disk drive (HDD).Although not illustrated, the console C is connected to a hospitalinformation system (HIS), a radiology information system (RIS), and/or apicture archiving and communication system (PACS) via a network N.

In this embodiment, the console C functions as an image processor.Hereinafter, the console C functioning as an image processor will bereferred to as image processor C. Alternatively, the image processor andthe console C may be provided in the form of separate units.

[Radiographic Image Capturing Devices]

The radiographic image capturing devices P used in the radiographicimage capturing system will now be described. FIG. 3 is a perspectiveview illustrating the exterior of a radiographic image capturing device.

The radiographic image capturing devices P according to this embodimenteach includes a casing 2 accommodating radiation detectors 7 and othercomponents described below. One of the side faces of the casing 2 isprovided with a power switch 25, a selector switch 26, the connector 27mentioned above, and indicators 28. Although not illustrated, forexample, the opposite side face of the casing 2 according to thisembodiment is provided with an antenna 29 (see FIG. 4) for wirelesscommunication with external units. A cable (not shown) can be connectedto the connector 27 to establish wire communication with an externalunit.

FIG. 4 is a block diagram illustrating the equivalent circuit of aradiographic image capturing device. With reference to FIG. 4, multipleradiation detectors 7 are disposed in a two-dimensional array or matrixon a sensor substrate (not shown) of a radiographic image capturingdevice P. The radiation detectors 7 each generate an electrical chargedepending on the intensity of radiation. The radiation detectors 7 areconnected to respective bias lines 9, which are connected to respectiveconnecting lines 10. The connecting lines 10 are connected to a biaspower supply 14. The bias power supply 14 applies an inverse biasvoltage to the radiation detectors 7 via the bias lines 9.

The radiation detectors 7 are connected to thin film transistors (TFTs)8, which serve as switching devices and are connected to respectivesignal lines 6. In a scan driver 15, a power circuit 15 a supplies ONand OFF voltages to a gate driver 15 b via a line 15 c. The gate driver15 b switches the ON and OFF voltages applied to lines L1 to Lx ofscanning lines 5. The TFTs 8 are turned on in response to an ON voltageapplied via the scanning lines 5 and cause the electrical chargeaccumulated in the radiation detectors 7 to be discharged via the signallines 6. The TFTs 8 are turned off in response to an OFF voltage appliedvia the scanning lines 5 to disconnect the radiation detectors 7 and therespective signal lines 6 and cause accumulation of the electricalcharges in the radiation detectors 7.

Multiple reader circuits 17 are provided in a reader IC 16 and connectedto the respective signal lines 6. During the reading process of imagedata D, electrical charges discharged from the radiation detectors 7flow into the reader circuits 17 via the signal lines 6, and voltagevalues corresponding to the electrical charges are output from amplifiercircuits 18. Correlated double sampling circuits (“CDSs” in FIG. 4) 19read the voltage values from the amplifier circuits 18 and output analogimage data items D corresponding to the voltage values to the componentsdownstream. The image data items D are sequentially sent to an A/Dconverter 20 via an analog multiplexer 21, converted to digital imagedata items D at the A/D converter 20, and then stored in a storage unit23.

A control unit 22 includes a computer (not shown) provided with a CPU, aROM, a RAM, and an input/output interface connected to a bus, and afield programmable gate array (FPGA). The control unit 22 may becomposed of a dedicated controller circuit. The control unit 22 isconnected to the storage unit 23 provided with a static RAM (SRAM), asynchronous DRAM (SDRAM), and a NAND flash memory.

The control unit 22 is connected to a communication unit 30 thatestablishes wired or wireless communication with external units via anantenna 29 or a connector 27. The control unit 22 is further connectedto an internal power supply 24, such as a lithium ion capacitor, thatsupplies electrical power to the functional units including the scandriver 15, the reader circuits 17, the storage unit 23, and the biaspower supply 14.

In this embodiment, each radiographic image capturing device P includesa sensor panel SP composed of a sensor substrate provided with multipleradiation detectors 7 and accommodated in a casing 2 (see FIG. 3). FIG.5 illustrates an example configuration of the sensor panel and a rearview of the sensor panel SP (the face opposite from the radiationdetectors 7). The front face of the sensor panel SP (provided with theradiation detectors 7) and the rear face (provided with the control unit22) are connected via flexible circuit boards FI. The flexible circuitboards FI are each provided with a reader IC 16 (see FIG. 4) and gateICs (not shown) constituting a gate driver 15 b.

[Processes Carried Out at Radiographic Image Capturing System DuringCapturing of Long Image by One-Shot Exposure]

The processes carried out at the console C and the radiographic imagecapturing devices P1 to P3 loaded in the holder 51 a of the capturingstand 51A during image capturing (i.e., the processes carried out beforeand after emission of radiation from the radiation irradiator 52 and theprocesses involving reading of image data D) are basically the same asknown processes carried out in simple radiography, and thus,descriptions thereon are omitted.

Upon reception of image data sets D from the radiographic imagecapturing devices P1 to P3 and an offset data set O corresponding to anoffset due to dark charges (also referred to as dark current) generatedin the radiation detectors 7, the console C calculates the true imagedata set D* by subtracting the offset data set O from the image data setD for each radiation detector 7 in each radiographic image capturingdevices P1 to P3 by expression (1), carries out precise imageprocessing, such as gain correction, defective pixel correction, andgradation processing corresponding to the captured site, on thecalculated true image data D*, to generate images p1 to p3 for therespective radiographic image capturing devices P1 to P3 (see FIGS. 22Aand 22B).

D*=D−O  (1)

Hereinafter, an image p generated on the basis of the image data Dacquired by a radiographic image capturing device P, as described above,is referred to as an image p acquired by a radiographic image capturingdevice P. As illustrated in FIGS. 22A and 22B, the image p acquired bythe rear radiographic image capturing device P among the images p1 to p3acquired as described above by the respective radiographic imagecapturing devices P1 to P3 in the holder 51 a contains transversestreaky components CL caused by linear structures, such as the edges ofthe casing 2 and the internal structure of the front radiographic imagecapturing device P and structural components CS caused by structures inthe casing of the front radiographic image capturing device P.

In the radiographic image capturing devices P loaded in the holder 51 aof the capturing stand 51A according to this embodiment, as illustratedin FIG. 6, the upper edge of the bottom front radiographic imagecapturing device Pb overlaps in the anteroposterior direction with thelower edge of the top rear radiographic image capturing device Pa, forexample.

The lower area of the image p acquired by the top rear radiographicimage capturing device Pa contains streaky components CL caused by thelinear edges at the top of the casing 2 b and the top of the sensorpanel SPb of the front radiographic image capturing device Pb andstructural components CS caused by structures inside the casing, such asthe reader IC 16 and the gate IC mounted on the flexible circuit boardFI (see FIG. 5) mounted on the sensor panel SPb of the frontradiographic image capturing device Pb. The reference signs La and Lb inFIG. 6 will be described below.

[Image Correction Process According to Present Invention]

An image correction process will now be described for the removal of thestructural components CS and the streaky components CL from images pacquired by the radiographic image capturing devices P loaded in theholder 51 a of the capturing stand 51A of the radiographic imagecapturing system 50 according to this embodiment. The operation of theradiographic image capturing system 50 according to this embodiment willalso be described.

As described above, the structural components CS and the streakycomponents CL are caused by the casing 2 and the internal structures ofthe front radiographic image capturing device P projected on the image pacquired by the rear radiographic image capturing device P in the holder51 a of the capturing stand 51A. At the capturing stands illustrated inFIGS. 1, 20A, and 21, the image p1 acquired by the radiographic imagecapturing device P1 contains projections of the casing 2 and otherstructures of the radiographic image capturing device P2, and the imagep2 acquired by the radiographic image capturing device P2 containsprojections of the casing 2 and other structures of the radiographicimage capturing device P3. The image p3 acquired by the radiographicimage capturing device P3 at least does not contain projections of thecasings 2 and other structures of the other radiographic image capturingdevices P.

At the capturing stand illustrated in FIG. 20B, the image p2 acquired bythe radiographic image capturing device P2 contains projections of thecasings 2 and other structures of the radiographic image capturingdevices P1 and P3, but the images p1 and p3 acquired by the radiographicimage capturing devices P1 and P3, respectively, at least do not containprojections of the casings 2 and other structures of the otherradiographic image capturing devices P.

What image p is to contain projections of the casings 2 and otherstructures of other radiographic image capturing devices P depends onthe layout of the radiographic image capturing devices P in the holder51 a of the capturing stand 51A. In the description below, the rearradiographic image capturing device P is referred to as the radiographicimage capturing device Pa, with reference to those exemplified in FIG.6, and the image p acquired by the radiographic image capturing devicePa contains projections of the casing 2 and other structures of thefront radiographic image capturing device Pb.

[Image Correction Process]

The image correction process according to this embodiment is carried outin accordance with the flow chart illustrated in FIG. 7. In the exampleflow illustrated in FIG. 7, the image correction process includesremoving the structural components CS from the image p and then removingthe streaky components CL remaining in the image p. Alternatively, thestreaky components CL may be removed from the image p and then thestructural components CS remaining in the image p may be removed. Thesteps in the image correction process carried out in accordance with theflow chart illustrated in FIG. 7 will now be described.

[Preliminary Acquisition of Calibration Image]

A calibration image “pcal” processed in Step S1 in the flow chart inFIG. 7 will now be described. In this embodiment, a calibration image“pcal”, such as that illustrated in FIG. 8, is generated through aprocess similar to that for the generation of an image p, as describedabove. That is, at least two radiographic image capturing devices Pa andPb are loaded in adjacent loading positions in the holder 51 a of thecapturing stand 51A (i.e., the radiographic image capturing devices Paand Pb are loaded in accordance with the layout illustrated in FIG. 6),radiation is emitted from the radiation irradiator 52 without thesubject, and the calibration image “pcal” is generated based on theimage data D acquired at the rear radiographic image capturing devicePa.

The calibration image “pcal” is a preliminarily captured image of thestructural components CS and the streaky components CL caused by theradiographic image capturing device P loaded at the front position inthe holder 51 a of the capturing stand 51A and projected on the image pacquired by the rear radiographic image capturing device P. Calibrationimages “pcal” are preliminarily generated for every radiographic imagecapturing device P loadable in the holder 51 a of the capturing stand51A.

For example, calibration images “pcal” for a radiographic imagecapturing device P are acquired before shipment of the device P and/orafter installation of the device P to a medical facility, such as ahospital. Alternatively, calibration images “pcal” may be acquiredperiodically or before every image capturing process. Identificationinformation or a cassette ID of the radiographic image capturing deviceP is written in the header of data on the calibration image “pcal” topreliminarily establish a correspondence between the radiographic imagecapturing device P and the calibration image “pcal”, and thiscorrespondence is preliminarily stored in a database stored in a storageunit Cb of the image processor C (see FIGS. 1 and 2) or a storage unitin a server (not shown).

In this embodiment, the image processor C removes the structuralcomponents CS caused by the front radiographic image capturing device Pbfrom the image p acquired by the rear radiographic image capturingdevice Pa through capturing of a subject by one-shot exposure. In thisremoval process, the image processor C removes the structural componentsCS caused by the front radiographic image capturing device Pb projectedon the image p on the basis of the calibration image “pcal” of the frontradiographic image capturing device Pb and the image p acquired by therear radiographic image capturing device Pa.

In this embodiment, the calibration image “pcal” is used in the step ofremoving the structural components in the image correction process.

[Loading Positions of Radiographic Image Capturing Device]

The radiographic image capturing device P that captures the calibrationimage “pcal” used for the removal of structural components is identifiedby the image processor C through determination of which one of theradiographic image capturing devices P is loaded in front of the rearradiographic image capturing device Pa during capturing of the image p.

For example, an operator or radiologist can instruct the image processorC to input cassette IDs of the radiographic image capturing devices Ploaded at respective loading positions Q1 to Q3 (see FIG. 9A describedbelow) in the holder 51 a of the capturing stand 51A.

Although not shown, barcodes or tags, such as two-dimensional codes orradio frequency identification (RFID) tags, that include informationsuch as the cassette IDs may be provided on the radiographic imagecapturing devices P, and readers may be provided at the loadingpositions Q1 to Q3 in the holder 51 a of the capturing stand 51A. Thecodes or tags on the radiographic image capturing devices P loaded tothe holder 51 a by the operator or radiologist can be automatically readwith the readers, and the identification information read by the readers(i.e., information on the loading positions) and the correspondingcassette IDs of the radiographic image capturing devices P loaded at therespective loading positions can be sent to the image processor C.

With reference to FIG. 9A, dongles Do1 to Do3 that store respectiveidentification information items are disposed at loading positions Q1 toQ3, respectively, in the holder 51 a of the capturing stand 51A. Withreference to FIG. 9B, the dongles Do are connected to connectors 27provided on the respective radiographic image capturing devices P beforethe radiographic image capturing devices P are loaded to the holder 51a. Once a dongle Do is connected to a radiographic image capturingdevice P, the radiographic image capturing device P may read theidentification information on the dongle Do (i.e., information on theloading positions) stored in the same dongle Do and send thisinformation together with the cassette ID of the radiographic imagecapturing device P to the image processor C.

[Calculation of Position and Enlargement Factor of CalibrationImage—Step S1]

The image processor C determines the image p to be corrected, i.e., theimage p acquired by the rear radiographic image capturing device Pa, onthe basis of the configuration of the holder 51 a of the capturing stand51A (i.e., the configuration illustrated in FIG. 1 or 20B) and theinformation on the loading positions Q1 to Q3 of the respectiveradiographic image capturing devices P1 to P3. Image correction iscarried out on all of the images p acquired by the rear radiographicimage capturing device Pa (for example, the two images p acquired by therespective radiographic image capturing devices P1 and P2 in FIG. 1, orthe image p acquired by the radiographic image capturing device P2 inFIG. 20B).

The image processor C identifies the radiographic image capturing devicePb loaded in front of the rear radiographic image capturing device Pa,which captured the image p from which the structural components are tobe removed, on the basis of the configuration of the holder 51 a of thecapturing stand 51A and the information on the loading positions Q ofthe radiographic image capturing devices P, and acquires the calibrationimage “pcal” for the identified radiographic image capturing device Pb.

The positional relationship between the front radiographic imagecapturing device Pb and the rear radiographic image capturing device Pa(i.e., the distance La between the lower edge of the sensor panel Spa ofthe rear radiographic image capturing device Pa (corresponding to thelower edge of the image p) and the upper edge of the casing 2 b of thefront radiographic image capturing device Pb and the distance Lb betweenthe sensor panels Spa and SPb of the respective radiographic imagecapturing devices Pa and Pb, as illustrated in FIG. 6) during capturingof the calibration image “pcal” does not necessarily coincide with thepositional relationship between the rear radiographic image capturingdevice Pa and the front radiographic image capturing device Pb duringthe actual capturing of a long image by one-shot exposure.

Although not shown, the distance SIDcal between the radiation irradiator52 and the radiographic image capturing device Pa (Pb) during capturingof the calibration image “pcal” also does not always coincide with thedistance SIDreal between the radiation irradiator 52 and theradiographic image capturing device Pa (Pb) during the actual capturingof a long image by one-shot exposure (see FIG. 1).

The image processor C adjusts the position of the image p and theposition of the calibration image “pcal” to match each other on thebasis of the information on the distances La and Lb during capturing ofthe calibration image written in the header of the calibration image“pcal” and the distances La and Lb during actual capturing of a longimage by one-shot exposure. The adjustment of the positions can becarried out not only in the vertical direction (distance La) and theanteroposterior direction (distance Lb) but also in the transversedirection orthogonal to these directions.

The image processor C adjusts the enlargement factor of the calibrationimage “pcal” to match the enlargement factor of the image p on the basisof the distance SIDcal during capturing of the calibration image and thedistance SIDreal during capturing of a long image by one-shot exposure,to generate an adjusted calibration image “pcal*”, as illustrated inFIG. 10.

[Removal of Structural Components—Step S2]

The image processor C removes the structural components from the imagep. In the removal of the structural components, the image processor Ccorrects the image p by appropriately increasing the pixel values f ofthe image p that are reduced due to the projection of structures, suchas ICs, of the front radiographic image capturing device Pb(corresponding to an area in the image p containing the structuralcomponents CS) through application of the base image “ppanel”, to removethe structural components CS from the image p.

Specifically, the image processor C generates a corrected image p by thefollowing expression (2):

g(x,y)=f(x,y)+A(x,y)×k(x,y)  (2)

where f(x,y) is a pixel value of a pixel (x,y) in the image p, k(x,y) isa pixel value of a pixel in the base image “ppanel”, A(x,y) is acoefficient, and g(x,y) is a pixel value of a pixel in the correctedimage p.

The image processor C generates a corrected image p by preparing abaseimage “ppanel” as described below. Specifically, the average value“have” is calculated as described above for the pixel values h(x,y) ofthe pixels in the area without streaky components CL and structuralcomponents CS in the adjusted calibration image “pcal*” (i.e., the toparea in the image “pcal*” illustrated in FIG. 10), and the pixel valuesk(x,y) of the pixels in the base image “ppanel” are calculated byexpression (3) for each pixel (x,y) in the adjusted calibration image“pcal*” containing the streaky components CL and the structuralcomponents CS:

k(x,y)=have−h(x,y)  (3)

where h(x,y) is a pixel value of a pixel (x,y) in the adjustedcalibration image “pcal*” (see FIG. 10).

Regarding the pixel values h (x,y) and k(x,y) in a pixel column in theadjusted calibration image “pcal*” (for example, a pixel column having awidth of one pixel extending in the vertical direction as illustrated inFIG. 10) and a pixel column in the base image “ppanel”, the pixel valuesh(x,y) of the adjusted calibration image “pcal*” substantially equal theaverage value “have” in areas without streaky components CL andstructural components CS but are smaller than the average value “have”in the areas containing the streaky components CL and the structuralcomponents CS, as illustrated in FIG. 11A, whereas the pixel valuesh(x,y) of the base image “ppanel” are substantially zero in areaswithout streaky components CL and structural components CS but arepositive values in the areas containing the streaky components CL andthe structural components CS, as illustrated in FIG. 11B.

The inventors have conducted a research and discovered that a mereincrease in the pixel values through addition of the pixel values k(x,y)of the pixels in the base image “ppanel”, which are calculated asdescribed above, and the pixel values f(x,y) of the pixels in the imagep, as calculated by expression (4), cannot completely remove the edgecomponents in the structural components CS (i.e., the boundary betweenthe structural components CS and other areas) and results in visiblynoticeable edge components remaining in the corrected image p.

g(x,y)=f(x,y)+k(x,y)  (4)

In this embodiment, the pixel values k(x,y) of the pixels in the baseimage “ppanel” to be added to the pixel values f(x,y) of the pixels inthe image p are multiplied by the coefficient A(x,y), which variesdepending on the intensity of the edge components of the structuralcomponents CS (i.e., the variation in the pixel values at the boundarybetween the structural components CS and other areas), before additionto the pixel values f(x,y) of the pixels in the image p, as defined byexpression (2), to precisely remove the structural components CS fromthe corrected image p.

The image processor C calculates the coefficient A(x,y) by assigning aregion of interest (ROI) of 100 by 100 pixels centered on one of thepixels (x,y) (i.e., a target pixel (x,y)) in the image p, as illustratedin FIG. 12, for example. The image processor C calculates evaluationfunctions e(x,y) for the pixels (x,y) in the ROI by expression (5), anddefines the coefficient A(x,y) as the minimum sum of the evaluationfunctions e(x,y) of the pixels (x,y) in the ROI.

e(x,y)={g(x+1,y)−g(x−1,y)}2+{g(x,y+1)−g(x,y−1)}2   (5)

The image processor C shifts the ROI in the image p and calculates thecoefficients A(x,y) for the pixels (x,y) in the image p. The actualcorrection of the pixel values f(x,y) of the pixels in the image p bythe expression (2) is only required in areas containing structuralcomponents CS and streaky components CL. Thus, the coefficients A(x,y)should only be calculated for such areas.

The area containing the structural components CS and the streakycomponents CL can be predetermined in the calibration image “pcal” todetermine the area in which the position and enlargement factor in thecalibration image “pcal” are adjusted as described above, i.e., the areain the image p containing the structural components CS and the streakycomponents CL. In this embodiment, the area in the image p containingthe structural components CS and the streaky components CL aredetermined, and an ROI is assigned to the pixels in the areas.

That is, in this embodiment, the image processor C removes thestructural components by calculating the values k(x,y) (i.e., the baseimage “ppanel”) to be added to the pixel values f(x,y) of the pixels(x,y) in areas in the image p containing the structural components CS(see FIG. 12) based on the calibration image “pcal*” (see FIG. 10). Theimage processor C removes the structural components by calculating thecorrected pixel values g(x,y) by adding the product of the coefficientsA(x,y) and the corresponding values k(x,y) to the pixel values f(x,y),as defined by expression (2).

For the determination of a coefficient A(x,y), an ROI containing atarget pixel (x,y) is assigned in the image p, as illustrated in FIG.12. The coefficient A(x,y) is then defined as the minimum sum of thevalues e(x,y) (i.e., the intensity of the edge component) calculated byexpression (5) (i.e., the evaluation factors) in the ROI.

In this embodiment, the image processor C removes the structuralcomponents as described above. Such a configuration allows appropriatecorrection of the image p and precise removal of the structuralcomponents CS from the image p.

At this point, complete removal of the streaky components CL is notaccomplished, and some streaky components CL remain in the correctedimage p. Thus, in this embodiment, the image processor C removes thestreaky components CL remaining in the corrected image p in a subsequentstep (Step S6 in FIG. 7).

[Correction of Concentration—Steps S3 to S5]

In this embodiment, the image processor C removes the remaining streakycomponents CL from the image p corrected as described above bytemporarily combining the corrected images p1 and p2 from which thestructural components Cs are removed as described above, the images p1and p2 being respectively acquired by radiographic image capturingdevices P1 and P2 vertically adjacent in the holder 51 a of thecapturing stand 51A, as illustrated in FIGS. 13A and 13B.

Specifically, the image processor C corrects the concentration of theimages p1 and/or p2 such that the concentration of the images p1 and p2match each other (Step S3 in FIG. 7), adjusts the positionalrelationship and the enlargement factors of the images p1 and p2 (StepS4), and overlays the identical regions of the subject in the images p1and p2, to smoothly connect the images p1 and p2 (Step S5).

Known schemes may be applied to the correction of concentration, theadjustment of positions and enlargement factors, and combination of theimages (Steps S3 to S5). Details of such schemes are disclosed inJapanese Patent Application Laid-Open Nos. 2002-44413, 2002-85392, and2002-94772, for example. The techniques described in thesespecifications are processes of combining images captured by computedradiography (CR) cassettes. These techniques can also be effectivelyapplied to processes of combining the images p captured by theradiographic image capturing devices P.

In a case where a radiographic image capturing device P3 is loaded at aloading position Q3 in the holder 51 a of the capturing stand 51A, theradiographic image capturing devices P1 and P2 are not projected on theimage p3 captured by the radiographic image capturing device P3. Thus,the image p3 should not require removal of structural components. Afterthe concentration is corrected (Step S3) and the positions andenlargement factor are adjusted (Step S4), the images p1, p2, and p3 arecombined.

In a typical process of generating a long image “plong” throughcombination of two images, the connecting area of the two images(overlapping area) contains only the image captured by the radiographicimage capturing device Pb, which is loaded at the front position in theholder 51 a of the capturing stand 51A (for example, the image capturedby the front radiographic image capturing device Pb in FIG. 6), and doesnot contain the image captured by the rear radiographic image capturingdevice Pa, which is loaded at the rear position in the holder 51 a ofthe capturing stand 51A, because the front radiographic image capturingdevice Pb may be projected on the connecting area (overlapping area) inthe image captured by the rear radiographic image capturing device Pa.

In this embodiment, the images p1 and p2 are temporarily combined toremove the streaky components. Thus, in the step of combining the images(Step S5), the connecting area (overlapping area) of the images p1 andp2 to be combined contain the remaining streaky components CL capturedby the radiographic image capturing devices P loaded in the rearpositions in the holder 51 a of the capturing stand 51A (i.e., theradiographic image capturing devices P1 and P2 respective to theradiographic image capturing devices P2 and P3), unlike the images usedin the process described above.

In this embodiment, the combined image “plong*” contains a streakycomponent CL remaining in the image p1 in the connecting area(overlapping area) of the two images (for example, images p1 and p2), asillustrated in FIG. 14. Although not shown, the connecting area of theimages p2 and p3 (overlapping area) also contains streaky components CLthat remained in the image p2.

Hereinafter, an image acquired through combination of images p, asdescribed above, is referred to as combined image “plong*” fordifferentiation from a long image “plong” combined through a typicalscheme.

[Removal of Streaky Components—Step S6]

The image processor C removes the streaky components CL residing orremaining in the combined image “plong*” on the basis of the combinedimage “plong*” generated as described above (Step S6 in FIG. 7). Theremoval of the streaky components CL from the connecting area of theimages p1 and p2 of the combined image “plong*” (see FIG. 14) will nowbe described. The streaky components CL in the connecting area of theimages p2 and p3 are also removed in a similar process.

In this embodiment, the streaky components are removed as follows. Thestreaky components CL can be regarded as horizontal low-frequencycomponents (along the y direction in FIG. 14) in the combined image“plong*”. With reference to FIG. 15, the image processor C extracts aregion R containing the streaky components CL in the combined image“plong*”, applies a low-pass filter, such as a Gaussian filter, in thehorizontal direction of the region R (i.e., a pixel row having a widthof one pixel extending in the horizontal direction), and smooths thestreaky components CL along the horizontal direction.

As described above, the area containing the streaky components CL in thecombined image “plong*”, i.e., the area containing the streakycomponents CL in the image p1, can be determined on the basis of thearea containing the streaky components CL in the calibration image“pcal”. Thus, the region R in the combined image “plong*” containing thestreaky components CL can be assigned to a region equivalent to the areacontaining the streaky components CL plus a predetermined number ofpixels added to the top and bottom edges, for example.

Smoothing of the streaky components CL through the low-pass filter canbe controlled and varied on the basis of information on the subject andedges in the pixel rows to be smoothed.

The region R of the combined image “plong*” passing through the low-passfilter along the horizontal direction contains the smoothed streakycomponents CL superimposed on background DC components. Thus, the imageprocessor C extracts the DC component from the region R of the combinedimage “plong*” after passing the combined image “plong*” through thelow-pass filter.

Specifically, with reference to FIG. 16, the image processor C selectspixel rows Lp1 and Lp2, each having a width of one pixel, from areasabove and below a region Rc containing the streaky components CL, inother words a region Rc other than the region containing the streakycomponents CL, within the region R containing the streaky components CL,in the combined image “plong*” passing through the low-pass filter.

The image processor C performs linear interpolation by expression (6),for example, on pixel values g(x,y) upper of pixels in the upper pixelrow Lp1 and corresponding pixel values g(x,y) lower of pixels in thelower pixel row Lp2 (i.e., pixels on different pixel columns at the samey coordinates), to calculate the pixel values g*(x,y) of the pixelsbetween the pixel rows Lp1 and Lp2.

g*(x,y)=t×g(x,y)upper+(1−t)×g(x,y)lower  (6)

where 0≦t≦1.

The image processor C carries out such calculation on the pixel columns(every y coordinate) in the region R of the combined image “plong*”passing through the low-pass filter, to extract the DC component fromthe region R (see FIG. 15). In the region R including areas above andbelow the pixel rows Lp1 and Lp2, respectively, as illustrated in FIG.16, the DC components of these areas are defined as the pixel valuesg(x,y) of the pixels in these areas.

If the image processor C selects pixel rows Lp1 and Lp2 of pixels havingsignificantly different pixel values g(x,y), the DC components acquiredthrough linear interpolation will be significantly different from theactual DC components. Thus, it is preferred that the image processor Cselects pixel rows Lp1 and Lp2 that have similar average pixel valuesg(x,y) of the pixels in the pixel rows Lp1 and Lp2, respectively.

With reference to FIG. 15, the image processor C subtracts the DCcomponents extracted as described above from the region R of thecombined image “plong*” passing through the low-pass filter, and removesthe background of the region R of the combined image “plong*” passingthrough the low-pass filter, to extract the streaky components CLresiding or remaining in the region R. That is, the DC componentsg*(x,y) of the pixels in the background (pixel values g(x,y) for pixelsin the areas above and below the pixel rows Lp1 and Lp2, respectively)are subtracted from the pixel values g(x,y) of the pixels in the regionR in the combined image “plong*” passing through the low-pass filter, toextract the streaky components CL.

The image processor C adds the extracted streaky components CL to thepixel values g(x,y) of the pixels corresponding to the combined image“plong*” (see FIG. 14), to remove the streaky components CL from thecombined image “plong*”.

In the removal of streaky components according to this embodiment (StepS6 in FIG. 7), the image processor C subtracts the DC components fromthe components acquired through the smoothing with a low-pass filteralong the horizontal direction of the region R containing the streakycomponents CL and assigned in an image p or the combined image “plong*”,to extract the streaky components CL (see FIG. 15), and adds theextracted streaky components CL to the pixel values g(x,y) of the pixelscorresponding to the image p or the combined image “plong*”, to removethe streaky components CL from the image p or combined image “plong*”.

In this embodiment, the image processor C removes the streaky componentsas described above to suitably correct the combined image “plong*” orimages p1 and p2, to precisely remove the streaky components CL residingor remaining in the combined image “plong*” or the images p1 and p2.

As a result of extracting the region R, which contains the streakycomponents CL, from an image p or the combined image “plong*”, andadding the streaky components CL extracted from the region R through theprocesses illustrated in FIG. 15 to the pixel values g(x,y) of thepixels corresponding to the image p or the combined image “plong*” (seeFIG. 14), as described above, the areas inside or outside the boundaryof the region R in the image p or the combined image “plong*” and/or thepixel rows Lp1 and Lp2 selected as described above could include afluctuation in pixel values.

In such a case, in the process of adding the streaky components CLextracted as described above to the image p or the combined image“plong*” from which the streaky components are removed, the products ofthe streaky components CL and a coefficient are added to the image p orcombined image “plong*” so as to prevent the fluctuation (orsignificantly reduce it to a non-visible level) and smooth the areas ofthe image p and the combined image “plong*” above and below thefluctuation (i.e., smoothing).

[Adjustment of Contrast and Granularity—Step S7]

Even after image correction is carried out as described above to removethe structural components CS and the streaky components CL (Steps S3 andS6) from the combined image “plong*” or images p1 and p2 (hereinafter,collectively referred to as combined image “plong*”), the contrast andgranularity of the areas in the combined image “plong*” from which thestructural components CS and the streaky components CL are removed mayhave contrast and granularity different from those of other areas in thecombined image “plong*”.

After the image processor C removes the structural components CS and thestreaky components CL from the combined image “plong*”, as describedabove, the contrast and granularity of the overall combined image“plong*” can be adjusted to matched values (Step S7 in FIG. 7). That is,the contrast and granularity of the areas of the combined image “plong*”from which the structural components CS and the streaky components CLare removed are matched to the contrast and granularity of the otherareas in the combined image “plong*” (in particular, the periphery ofthe removed structural components CS and streaky components CL). Suchimage processing can be performed to match the contrast and granularityof the different areas in the combined image “plong*”, making the areasin the combined image “plong*” from which the structural components CSand the streaky components CL are removed indistinguishable from theother areas.

The contrast and granularity can be adjusted so that the horizontallines above and below the seam of combined images have similar frequencycomponents, for example. Specifically, (1) high-frequency componentsabove the seam are blurred or smoothed; (2) an unsharp mask is appliedbelow the seam to enhance the high-frequency components; and (3) thehigh-frequency components above and below the seam are measured andadjusted to match each other. The process returns to step (1) andrepeated, as necessary. In step (3), a Fourier transform spectrum orother statistical indices may be used as a measurement index.

In another scheme, the amplification factors of the contrast andgranularity can be preliminarily defined in each area that containsstructural components CS and streaky components CL caused by theprojection of the front radiographic image capturing device Pb in theimage p captured by the rear radiographic image capturing device Pa; theareas in the image p from which the structural components CS and thestreaky components CL are removed as described above are resolved intolow, intermediate, and high frequency image components; and the productof the intermediate frequency image components and the amplificationfactor of contrast, the product of the high frequency image componentsand the amplification factor of granularity, and these products areadded to the low frequency image components, to achieve uniform contrastand granularity.

The amplification factors of the contrast and granularity may be 1 ormore or less than 1. An amplification factor of 1 or more enhancescontrast and granularity, whereas an amplification factor of less than 1smooths contrast and granularity. The high frequency information removedfrom the image after adjustment can be recovered through the use of aWiener filter. Such a technique is effective in making anindistinguishable seam between images having different qualities.

[Generation of Long Image]

As described above, the image processor C corrects the combined image“plong*” through removal of structural components and streaky componentsand adjusts the contrast and granularity, as required, to acquire acombined image “plong*” equivalent to a long image “plong”, such as thatillustrated in FIG. 17. Thus, the image processor C can generate a longimage “plong” through image correction on the combined image “plong*”,as described above.

As described above, in the generation of a typical long image “plong”through combination of images p1 and p2 (or images p1 to p3), theconnecting area (overlapping area) of the images p contain an imagecaptured by the radiographic image capturing device Pb loaded in thefront position in the holder 51 a of the capturing stand 51A (forexample, the image captured by the front radiographic image capturingdevice Pb in FIG. 6). In contrast, in the connecting step (Step S5) inthe image correction process according to this embodiment (see FIG. 7),the connecting area (overlapping area) of the images p contains an imagep captured by the radiographic image capturing device Pa loaded in therear position in the holder 51 a of the capturing stand 51A.

Alternatively, in this embodiment, a long image “plong” can be generatedin accordance with the process of generating a typical long image“plong”.

[Segmentation—Step S8]

In this embodiment, the image processor C corrects the combined image“plong*” through removal of structural components and streakycomponents, as described above, adjusts the contrast and granularity, asrequired, and segments the processed combined image “plong*” into imagesp1 to p3 (Step S8 in FIG. 7). To differentiate the images p1 to p3captured by the radiographic image capturing devices P1 to P3,respectively, loaded in the holder 51 a of the capturing stand 51A, theimages acquired through segmentation of the processed combined image“plong*” will hereinafter be referred to as images p*1 to p*3.

In the segmentation (Step S8), the image processor C segments theprocessed combined image “plong*” at the bottom edges of the images p1and p2, as illustrated in FIG. 18A, prior to combination (see FIGS. 13Aand 13B) to generate images p*1 to p*3. Simple segmentation of theprocessed combined image “plong*” could cause loss in the image p*2 inthe overlapping area of the images p1 and p2, which are combined afterthe concentration correction (Step S3 in FIG. 7) and the adjustment ofthe position and enlargement factor (Step S4). Similarly, a portion ofthe image p*3 could be lost in the overlapping area of the images p2 andp3 that are combined.

Among the images p*1 to p*3 generated through the segmentation of theprocessed combined image “plong*,” a portion of the image p*2corresponding to the overlapping area of the combined images p1 and p2and a portion of the image p*3 corresponding to the overlapping area ofthe combined images p2 and p3 are respectively added to the top edges ofthe images p*2 and p*3, which are generated through segmentation.

In this embodiment, the images p*1 and p*2 generated by the imageprocessor C through segmentation of the combined image “plong*”, asillustrated in FIG. 18B, are derived from the images p1 and p2 throughremoval of the structural components CS and the streaky components CL(and the adjustment of the contrast and granularity, as required).

In other words, the structural components CS and the streaky componentsCL can be precisely removed from the images p1 and p2 acquired by therear radiographic image capturing devices P1 and P2, respectively,loaded in the holder 51 a of the capturing stand 51A. Since thesegmented image p*3 does not contain structural components CS andstreaky components CL in the first place, the segmented image p*3 isidentical to the original image p3.

Advantageous Effects

In the radiographic image capturing system 50 according to thisembodiment as described above, the image processor C can remove thestructural components CS and the streaky components CL (see FIGS. 12,22A, and 22B) caused by the front radiographic image capturing device Pbprojected on the image p acquired by the rear radiographic imagecapturing device Pa loaded in the holder 51 a of the capturing stand 51Afor capturing a long image by one-shot exposure (see FIG. 6).

By image correction on the image p, the images p acquired throughcapturing of a long image by one-shot exposure can be preciselycorrected, and images p*1 to p*3 (see FIG. 18B) can be acquired throughprecise removal of the structural components CS and the streakycomponents CL from the corrected images p. The images p*1 to p*3 can becombined to precisely generate a long image “plong” (see FIG. 17).

In contrast to the embodiment described above, image correction can becarried out by removing the streaky components in the images p and thenremoving the structural components CS remaining in the images p, asdescribed above.

In the embodiment described above, the images p1 to p3 acquired by therespective radiographic image capturing devices P1 to P3 loaded in theholder 51 a of the capturing stand 51A during image capturing aretemporarily combined by the image processor C, and streaky componentsare removed from the combined image “plong*” (Step S6 in FIG. 7).Alternatively, as illustrated in FIG. 19, for example, the streakycomponents can be removed from the images p1 and p2 without combinationof the images p1 to p3.

In the embodiment described above, as illustrated in FIG. 16, the pixelrow Lp1 having a width of one pixel is selected from the image p1, andthe pixel row Lp2 having a width of one pixel is selected from the imagep2. The pixel rows Lp1 and Lp2 are linearly interpolated by expression(6) to calculate the DC components, which are background components ofthe region R required for the removal of streaky components.Unfortunately, the removal of the streaky components from each of theimages p1 and p2, as described, precludes the selection of at least thepixel row Lp2 having a width of one pixel.

In such a case, for example, the streaky components can be removed fromeach of the images p1 and p2 as in the embodiment described above usingdata on a pixel row having a width of one pixel at the top of the imagep2 for the removal of the streaky components from the image p1 and usingdata on a pixel row having a width of one pixel at the top of the imagep3 for the removal of the streaky components from the image p2.

For example, during removal of the streaky components from the image p1,pixel rows Lp1 and Lp2 both having a width of one pixel may be selectedfrom the image p1 above a range Rc (see FIG. 16), and the pixel row Lp2can be presumed to be present in the image p1 below the range Rc, asillustrated in FIG. 16. In this way, the streaky components can beremoved from each of the images p1 and p2 as in the embodiment describedabove.

[Images without Projection of Structural Component]

Depending on the structure of the front radiographic image capturingdevice Pb (see FIG. 6) loaded in the holder 51 a of the capturing stand51A, the image p captured by the rear radiographic image capturingdevice Pa could contain the streaky components CL without the structuralcomponents CS or with structural components CS which are hardly visible.

In such a case, as in the embodiment described above, the images p1 top3 can be combined to remove the streaky components, or the streakycomponents can be removed from each of the individual images p1 and p2without combination of the images p1 to p3. In such a case, the Steps S1and S2 in the flow chart illustrated in FIGS. 7 and 19, for example, areunnecessary, and thus the calibration image “pcal” is also unnecessary.The removal of the streaky components is then carried out as illustratedin FIG. 15.

In the removal of streaky components from a combined image “plong*”generated through the combination of the images p1 to p3 or from each ofthe individual images p1 and p2 without combination of the images p1 top3, image processing is carried out as described above to match (enhanceor smooth) the contrast and granularity in the areas of the combinedimage “plong*” or the images p1 and p2 from which the streaky componentsCL are removed to the other areas of the combined image “plong*” or theimages p1 and p2 (in particular, the periphery of the removed structuralcomponents CS and streaky components CL).

Through such configuration, areas in the combined image “plong*” or theimages p1 and p2 from which the structural components CS and the streakycomponents CL are removed can be indistinguishable from other areas, asdescribed above.

The present invention is not limited to the above embodiments andmodifications, and can be suitably changed without leaving the scope ofthe present invention.

This application is based upon and claims the benefit of priority fromthe Japanese Patent Application No. 2015-082439, filed Apr. 14, 2015,the entire contents of which are incorporated herein by reference.

What is claimed is:
 1. A radiographic image capturing system comprising:a capturing stand which includes a holder which is able to hold aplurality of radiographic image capturing devices; a radiationirradiator which is able to irradiate the radiographic image capturingdevices loaded in the holder at once with radiation; and an imageprocessor which generates a plurality of images based on image dataacquired by the radiographic image capturing devices, wherein, an edgeof a front radiographic image capturing device overlaps in ananteroposterior direction with an edge of a rear radiographic imagecapturing device in the holder in view from the radiation irradiator,the front radiographic image capturing device being a radiographic imagecapturing device close to the radiation irradiator among theradiographic image capturing devices loaded in the holder, the rearradiographic image capturing device being a radiographic image capturingdevice remote from the radiation irradiator among the radiographic imagecapturing devices loaded in the holder, the image processor removes astructural component derived from the front radiographic image capturingdevice projected on a generated image, on the basis of a calibrationimage and the generated image, the calibration image being preliminarilygenerated based on the image data acquired by the rear radiographicimage capturing device irradiated with radiation with no subjectdisposed in front of the radiographic image capturing devices loaded inthe holder of the capturing stand, the generated image being generatedbased on the image data acquired by the rear radiographic imagecapturing device during actual image capturing of a subject, and theimage processor removes a streaky component residing in the generatedimage on the basis of the generated image, to correct the image.
 2. Theradiographic image capturing system according to claim 1, wherein, theimage processor corrects the image through removal of the structuralcomponent and removal of the streaky component remaining in the imageafter the removal of the structural component.
 3. The radiographic imagecapturing system according to claim 2, wherein, the image processorremoves the structural component from each image generated based on theimage data acquired by each radiographic image capturing device loadedin the holder of the capturing stand, combines the images from which thestructural component is removed, and removes the streaky componentremaining in a combined image generated by combining the images.
 4. Theradiographic image capturing system according to claim 3, wherein, theimage processor combines the images at an overlapping area of theimages, the overlapping area including the image captured by the rearradiographic image capturing device in the holder of the capturingstand.
 5. The radiographic image capturing system according to claim 1,wherein, the image processor corrects the image through removal of thestreaky component and removal of the structural component remaining inthe image after the removal of the streaky component.
 6. Theradiographic image capturing system according to claim 1, wherein,during removal of the structural components, the image processor,calculates a value k(x,y) based on the calibration image, the valuek(x,y) being added to a pixel value f(x,y) of a pixel (x,y) in an areaof the image on which the structural component of the front radiographicimage capturing device is projected, calculates a corrected pixel valueg(x,y) determined by adding the product of the value k(x,y) and acoefficient A(x,y) to the pixel value f(x,y), as defined by anexpression (1), to remove the structural component:g(x,y)=f(x,y)+A(x,y)×k(x,y)  (1), and determines the coefficient A(x,y)as a minimum sum of a value e(x,y) calculated by an expression (2)within a region of interest assigned to include a target pixel on theimage:e(x,y)={g(x+1,y)−g(x−1,y)}² +{g(x,y+1)−g(x,y−1)}²  (2)
 7. Theradiographic image capturing system according to claim 1, wherein,during removal of the streaky component, the image processor, subtractsa background component from a component acquired through horizontalsmoothening of a region assigned in the image containing the streakycomponent, to extract the streaky component, and adds the extractedstreaky component to a pixel value of each pixel in the image, to removethe streaky component from the image.
 8. The radiographic imagecapturing system according to claim 1, wherein, the image processorcorrects the image and carries out image processing to adjust contrastand granularity of an area of the image from which the structuralcomponent and the streaky component are removed to match the contrastand granularity with another area in the image.
 9. The radiographicimage capturing system according to claim 8, wherein, the process ofadjusting the contrast and the granularity of the image includesresolving an area of the corrected image from which the structuralcomponent and the streaky component are removed into images havingdifferent frequency bands, multiplying the images having differentfrequency bands with a predetermined amplification factor, and addingtogether the images having different frequency bands multiplied with theamplification factor.
 10. A radiographic image capturing systemcomprising: a capturing stand which includes a holder which is able tohold a plurality of radiographic image capturing devices; a radiationirradiator which is able to irradiate the radiographic image capturingdevices loaded in the holder at once with radiation; and an imageprocessor which generates a plurality of images based on image dataacquired by the radiographic image capturing devices, wherein, an edgeof a front radiographic image capturing device overlaps in ananteroposterior direction with an edge of a rear radiographic imagecapturing device in the holder in view from the radiation irradiator,the front radiographic image capturing device being a radiographic imagecapturing device close to the radiation irradiator among theradiographic image capturing devices loaded in the holder, the rearradiographic image capturing device being a radiographic image capturingdevice remote from the radiation irradiator among the radiographic imagecapturing devices loaded in the holder, the image processor removes astreaky component residing in the generated image based on the generatedimage, to correct the image, and the image processor subtracts abackground component from a component acquired through horizontalsmoothing of a region assigned in the image containing the streakycomponent during removal of the streaky component, to extract thestreaky component, and adds the extracted streaky component to a pixelvalue of each pixel in the image, to remove the streaky component fromthe image.
 11. The radiographic image capturing system according toclaim 10, wherein, the image processor corrects the image and carriesout image processing to adjust contrast and granularity of an area ofthe image from which the streaky component is removed to match thecontrast and granularity with another area of the image.
 12. Theradiographic image capturing system according to claim 11, wherein, theprocess of adjusting the contrast and the granularity of the imageincludes resolving an area of the corrected image from which the streakycomponent is removed into images having different frequency bands,multiplying the images having different frequency bands with apredetermined amplification factor, and adding together the imageshaving different frequency bands multiplied with the amplificationfactor.